On what basis a convergent-divergent nozzle is designed?

This nozzle configuration is called a convergent-divergent, or CD, nozzle. In a CD nozzle, the hot exhaust leaves the combustion chamber and converges down to the minimum area, or throat, of the nozzle. The throat size is chosen to choke the flow and set the mass flow rate through the system.

What is choked flow for a converging diverging nozzle?

Choked flow is a fluid dynamic condition associated with the venturi effect. When a flowing fluid at a given pressure and temperature passes through a constriction (such as the throat of a convergent-divergent nozzle or a valve in a pipe) into a lower pressure environment the fluid velocity increases.

What is convergent and divergent nozzle?

Convergent-divergent nozzle. An arrangement in which the forward portion of the nozzle is convergent, which increases the pressure of the exhaust gases, while the aft section is divergent to increase gas velocity to the supersonic speed and avoid losses from underexpansion.

Why are convergent-divergent nozzles used?

Convergent-divergent type of nozzles are mostly used for supersonic flows because it is impossible to create supersonic flows (mach number more than one) in convergent type of nozzle and therefore it restricts us to a limited amount of mass flow through a particular nozzle.

How do you stop choked flow?

To resolve choked flow, you must lower the differential between upstream and downstream pressure. If you have 1,000 PSI upstream and 500 PSI downstream, you could increase downstream pressure to eliminate choked flow. The exact amount to exit choked flow is affected by flow rate, temperature and fluid specific gravity.

Where is convergent nozzle used?

Few examples of the application of convergent divergent type of nozzles in engineering are: *Steam turbines : In power plants . *Rockets : for providing sufficient thrust to move upwards. *The supersonic gas turbine engine : for the air intake when air requirement of engine is high.

What are the convergent nozzle?

A convergent nozzle is a nozzle that starts big and gets smaller-a decrease in cross-sectional area. As a fluid enters the smaller cross-section, it has to speed up due to the conservation of mass. To maintain a constant amount of fluid moving through the restricted portion of the nozzle, the fluid must move faster.

Why does Shockwave appear in convergent-divergent nozzles?

The location of the shock is such that the pressure at the diverging section exit will equal the back pressure. Oblique shock waves appear outside the nozzle because the flow static pressure at the exit is lower than the back pressure and so the flow must be compressed to eventually reach the back pressure.

When does converging diverging nozzle reach its maximum speed?

The flow accelerates out of the chamber through the converging section, reaching its maximum (subsonic) speed at the throat. The flow then decelerates through the diverging section and exhausts into the ambient as a subsonic jet. Lowering the back pressure in this state increases the flow speed everywhere in the nozzle.

How does a converging nozzle in a jet engine work?

This region of supersonic acceleration is terminated by a normal shock wave. The shock wave produces a near-instantaneous deceleration of the flow to subsonic speed. This subsonic flow then decelerates through the remainder of the diverging section and exhausts as a subsonic jet.

Why is a divergent nozzle used in supersonic engines?

The flow in the throat is sonic which means the Mach number is equal to one in the throat. Downstream of the throat, the geometry diverges and the flow is isentropically expanded to a supersonic Mach number that depends on the area ratio of the exit to the throat.

What happens to the Mach number of a nozzle?

In a steady internal flow (like a nozzle) the Mach number can only reach 1 at a minimum in the cross-sectional area. When the nozzle isn’t choked, the flow through it is entirely subsonic and, if you lower the back pressure a little, the flow goes faster and the flow rate increases.